Goofs
There's a lot about the dream world that doesn't make sense. Why didn't the dream world give Diggle and Sara their perfect lives, like it did Oliver, Thea and - to a point - Ray? While John wasn't exactly unhappy as The Hood until Oliver showed up, it's hard to believe he wouldn't have Lyla or John Jr. in his life. Ditto Sara seemingly not having any role other than to revel in her sister's happiness. Were The Dominators too cheap to generate each of the heroes their own perfect world? Was the confusion meant to prolong their time in the dream world as their minds were read? Why bother with hostile memories which threatened the reality of the dream world? And why bother having a portal out of the dream world in the first place?

When did Cisco get a piece of the Dominator's ship? (Possibly a scene that was cut for time?)

Why has Wild Dog's sudden hatred of super-powered people never come up regarding the guy wearing the magical costume made of rags who is on his team?

The villain of the week is beaten far too easy and serves no purpose other than to give Supergirl and The Flash a chance to show off.

Why does the dream world create ghosts of two people who haven't died - Felicity and Roy Harper - as Ollie is about to leave? (I know this was the only way they could give Roy Harper an appearance in the episode, but it doesn't make sense in the logic of the world.)

Cisco says that geographical coordinates don't have negative numbers. In fact, negative numbers are used to note areas south of the equator in latitude and west of the prime meridian in longitude.

Performances
Stephen Amell gives one of his best performances ever, trying to say good-bye to the parents he lost as he breaks away from a perfect world. It gets even better later on, opposite Willa Holland, as she makes a convincing case for staying in the dream world and allowing themselves to be happy for once. It's a heartbreaking moment and a great performance for both actors.

Artistry
The editing team did a fantastic job of patching together the various clips for the flashback sequences.

The special effects for the Flash and Supergirl vs. Dr. Washington fight are top-notch.

Trivia
As the title suggests, the main inspiration for this four-part crossover event between all of the DCTVU shows was the 1988 crossover event Invasion!

Invasion! was based around the idea that an alliance of alien worlds - led by The Dominators - attacked Earth due to their concerns that Earth's growing metahuman population would become a threat to their planets.

The Dominators in the original comics had yellow skin, a red circle in the middle of their foreheads, claw-like fingernails and sharp fang-like teeth.

The DCTVU version of The Dominators resemble the comic-book counterpart for the most part, save that their skin is more grey than yellow. Also, they do not wear clothing, which the comic book Dominators did.

This episode was the 100th episode of Arrow.

This episode was the third part of a four-part crossover between all of The CW Network's DC Comics superhero shows.

The story for this episode greatly resembles the plot of Perchance To Dream - an episode of Batman: The Animated Series. In that episode, Bruce Wayne finds himself in a world where his parents are alive, Selina Kyle is his fiancee and he is no longer Batman, though he starts to have feelings that he was Batman after seeing Batman in the street. He eventually realizes he's in an illusion - one crafted by The Mad Hatter to give him a perfect life.

In this episode,Oliver Queen's parents are both alive and he is about to be married to Laurel Lance. He is no longer Green Arrow, but has visions of being Green Arrow after having an encounter with The Hood in the street. He eventually realizes he's an illusion - one crafted by The Dominators to keep him distracted.

There are a number of other common plot-beats between the two shows, including the search for an entrance to a hidden superhero hideout, an attempt to unmask one's own superhero alter ego and an incongruous building (a clock tower in Perchance To Dream, the Smoak Electronics building in Invasion!) leading to the way out of the dream world.

The story for this episode also resembles the classic Alan Moore Superman story For The Man Who Has Everything. In that comic, Superman falls prey to a parasitic plant called The Black Mercy that causes its host to hallucinate their perfect world as the plant feasts upon their body. As in that story, any attempt to resist the reality created by The Black Mercy results in the dream world attacking the host or the host's loved ones appearing and begging them not to leave them.

Oliver name-drops the story, saying at one point that "he has everything."

For The Man Who Has Everything was adapted for the Supergirl TV series in S113 - For The Girl Who Has Everything.
In the comics, Oliver Queen had his own encounter with a Black Mercy plant in Green Lantern (Volume 4) #7 and #8. In that story, both Hal Jordan and Oliver Queen were attacked by a Black Mercy that primarily focused on Hal Jordan, creating a perfect world for Oliver Queen based on what Hal thought Ollie's perfect world would be like. Oliver Queen saw through the illusion and as able to break both of them free of the dream world. Something similar happens here, with John Diggle and Sara Lance both realizing there's something wrong with the supposedly perfect reality they are part of.

Curtis Holt expresses reservations about the idea of a divine plan that includes space monsters. This is a nod to the JSA comics where Mister Terrific was a staunch atheist despite working with colleagues who claimed to have powers granted by divine and magical sources.

In the dream world, Malcolm Merlyn says that Tommy Merlyn couldn't make it to the wedding because he's working triple-shifts in his new job as a doctor in Chicago. This is a nod to how actor Colin Donnell - who played Tommy Merlyn in the first season of Arrow - is now playing the role of Dr. Connor Rhodes on Chicago Med, Chicago P.D. and Chicago Fire and was unable to do a cameo in this episode due to his busy schedule.

Felicity tracks the location of Team Arrow to -3.127 Latitude, - 23.7987 Longitude. This indicates somewhere in the middle of the Atlantic Ocean... or above it.

Technobabble

The first attempt to hack the Dominator technology fails because the team tried to plug human technology into a Dominator power source. This caused a power overload, which requires them to find a regulator.

Van Horn industries developed a prototype regulator for NASA. It was perfected, but it was stolen by a Dr. Laura Washington - a scientist who has been augmenting her body with various stolen electronic implants. The implants give her enhanced strength, stamina and electricity-based powers.

The martial art Sara uses to fight Deathstroke in the dream world is Jeet Kune Do - a hybrid martial art heavily influenced by the martial arts philosophy of Bruce Lee.

Rory Regan identifies the "soup" created by Curtis' translator as Gamatria - a Kabbalistic method of interpreting the Hebrew scriptures by computing the numerical value of words, based on those of their constituent letters. In Hebrew, each letter has a numerical value. Gamatria is the calculation of the numerical equivalents of letters, words or phrases.

Felicity tracks the location of Team Arrow to -3.127 Latitude, - 23.7987 Longitude. This indicates somewhere in the middle of the Atlantic Ocean.

Ray examines the technology The Dominators were using to keep them under and determined it used a neuromorphic interface similar to what he used to control the ATOM suit. This means The Dominators may have been probing their subconscious for intel while the shared hallucination kept their minds occupied. Ray further theorizes that the five of them (Sara, Diggle, Thea, Oliver and himself) were abducted because they were ordinary humans.

Gideon translates "Klic-Clac-To Nick-Lava Shack-too" to "We are nearing completion of the weapon."

The Flash: What's your damage, man?Wild Dog: My damage is that people like you two have the power of gods yet you think you can make the world a better place just by putting on a fancy costume.Supergirl: No! We... we think we make the world a better place because, well... well, we do!

Ollie: These head games aren't over. They are going to push back against whatever we do.John: Push back? Like how?(Oliver looks to one side, where Deathstroke emerges from the bushes, twirling a sword.)Ollie: Like that.

(Sara Lance catches Deathstrike's sword arm, disarms him and runs him through with his own sword. She then looks down in astonishment, holding the katana in a defensive kata whilst in her bridesmaid dress.)Sara: How did I do that?

Thea: It's too bad Tommy couldn't make it, though.Merlyn: Well, they've got him working triple shifts at the hospital these days. Besides, Chicago isn't exactly next door.Thea: I can't believe he's a doctor now.Merlyn: Well, he says the same thing about you, Miss Entrepreneur.Thea: I don't think running Verdant makes me an entrepreneur.Merlyn: No, but it makes you successful. Your father should be very proud of the woman you've grown into.

(Moira and Robert Queen try to talk Ollie into getting ready for the wedding.)Moira: This is your life now.(Oliver sighs and steadies himself.)Oliver: No, it isn't.(Oliver hugs Moira tightly.)Moira: Oliver?(Oliver moves to hug his father, fighting back the tears.)Oliver: I'm so... I'm sorry.(Oliver lets go of Robert and walks to where Thea and Sara are standing in one corner of the room.)Oliver: Speedy...Sara: She knows, Ollie. She knows and she doesn't want to go!Thea: The better question is why would you want to?Sara: Because none of this is real.Thea: It's real enough, ok? (tearing up) It's - it's better than our real lives. In -in this life, Laurel is alive. My parents are alive...Sara: But those are not your parents!Thea: They remember the only lullaby that would actually work to put me to sleep. They remember every day of my life, okay? They even smell like them, Ollie!Oliver: They're not them, Thea. I want them to be. But they're not. (To Sara) Where are John and Ray?Sara: They're waiting outside.Oliver: Give us a few minutes.(Sara nods and heads for the exit.)Oliver: We can't stay here, Speedy. No matter how much we want to, we can't.Thea: Why not? What is waiting for us wherever we are right now? Nothing. Nothing but pain and suffering.Oliver: Thea, we have responsibilities. We have people who count on us.Thea: There's Flash and Supergirl and people with actual powers now. Whatever needs to be done, they can handle it. We - we finally have a chance to be happy. I mean, why - why can't you just for a second accept that maybe this is your reward for all the sacrifices you have made?Oliver: I didn't make those sacrifices for a reward Thea. I did what I did because I thought it was right. And seeing all this... it has just... it has shown me that there is so much more to do. So please - I'm begging you to come with me because I cannot do it alone.Thea: But... I can't lose them again. I can't lose my family.(Oliver just stares at her but finally nods.)
Oliver: Okay. Okay. All right.(Ollie hugs her)Oliver: I want you to be well. I want you to be happy. I love you, Thea.(Ollie lets go of her and leaves, leaving Thea alone.)

Dialogue DisastersWild Dog: Super powers are evil, man. And I don't want anything to do with them. Or with either of you.

Wild Dog: If super powers are a thing, it's good that there are guys like you to help the world.

Continuity
The episode opens with a scene of Oliver running through the woods on the Queen Manor estate. This mirrors the opening shot in the first episode, where Oliver was seen running through the forest on Lian Yu.

Rory tells the rest of Team Arrow that Felicity called him and told him that Oliver, Thea and Diggle had been abducted by aliens. This happened in F308.

When introduced to Rory Regan, Cisco says that makes him the second Rory he knows and the first one that isn't a douche. This is a reference to Mick Rory a.k.a. Heatwave.

Cisco uses his Vibe powers on one of Oliver's old broken bows to locate him. This gives him a vision of Oliver and company in some kind of statsis pod in some kind of alien environment.

Wild Dog has a hatred of metahumans. For some reason, it doesn't seem to apply to Ragman.

In the dream world, Thea gives Oliver a hozen as a gift before the wedding rehearsal dinner. This is the same arrowhead neclace that Oliver gave Thea in the first episode,

In the dream world, Robert Queen has just been elected mayor of Starling City and Oliver is supposed to take over Queen Consolidated when he takes office in two months.

In the dream world, Star City it is still called Starling City.

Oliver suggests Walter Steele take over as CEO instead of him. In the original universe, Walter Steele did take over Queen Consolidated after Robert Queen's death and married Moira Queen.

Oliver briefly has visions of his father's death and the sinking of The Queen's Gambit from the first episode,

Oliver briefly has a vision of Laurel as she appeared before she died in the hospital in 418.

In the dream world, Quentin Lance is still a Captain in the CCPD and he likes Oliver Queen.

Oliver briefly has visions of his establishing his first Arrow-cave and confronting Quentin for the first time as The Hood in the first episode,

Looking at a map of Starling City, Oliver briefly has visions of his campaign for Mayor of Star City during Season Four and the secret passageway to The Bunker in his campaign headquarters.

Sara Lance claims to only like girls. This may be a side-effect of The Flashpoint Reality because she had been bisexual during the first four seasons of Arrow and the first season of Legends of Tomorrow.

In the dream world, Ray Palmer is a business associate of Robert Queen, who is trying to put in a bid to take over Queen Consolidated. He is engaged to Felicity Smoak, though he has memories about his fiancee being a woman named Anna.

Both Sara Lance and Ray Palmer have visions of each other and their time together on The Waverider when they "meet for the first time" at the rehearsal dinner. The scenes of their visions include their first time riding on The Waverider together (L101), the two walking down a street in 1940s New York (L201) and a fight in the League of Assassin's headquarters (L109).

A Merlyn Global Group building is visible in the Starling City skyline.

While being strangled by The Hood, Oliver has visions of his meeting John Diggle (101), Diggle angrily driving after Ollie snuck off (102) agreeing to take him on as a partner (104), the two of them eating at Big Belly Burger together (103), John's wedding to Lyla Hall (317), the death of Andy Diggle (420) and John Diggle calling Oliver his brother (407).

Oliver also has visions of Felicity Smoak. The visions depict the first time he saw her (103), their first date (301), their first kiss (301), their first time making love (320), her near death at the hands of Damien Darhk's men (409) and their fake wedding (416).

In the dream world, John Diggle is The Hood and is working with Felicity Smoak out of The Bunker. He says he became The Arrow after returning from serving in the 105th Airborne out of Kandahar. He did things he wasn't proud of and came home to atone for his actions.

In the dream world, Andy Diggle is still alive and working in personal security.

While hugging Moira Queen, Thea has a vision of Moira's death from 220.

Diggle makes reference to a Russian lady downstairs when he intrudes on Oliver and Laurel. This is a reference to Rasia - a house-keeper in the Queen household staff, first seen in 101,who apparently did more to raise Oliver Queen than his mother did.

The creature that Diggle draws from one of his dream flashes is a Dominator.

Sara Lance knows Jeet Kune Do.

Sara Lance has a vision of the battle between The Flash and Green Arrow vs. The rest of The Legends and Team Arrow from F308. She also remembers Oliver, Thea, Diggle, Ray and herself being abducted by The Dominators.

In the dream world, Tommy Merlyn apparently moved to Chicago after getting his medical degree.

In the dream world, Thea is still running the night club Verdant.

Oliver has another vision from the first episode, after his father uses the phrase "that is not going to finish well".

The Smoak Technologies building was first seen in the Star City of 2046 in L106.

Before leaving the dream world, Oliver has visions of various friends and family, who speak lines about who he really is and how much they meant to him. These include Moria Queen calling Oliver "her beautiful boy" and saying "she could not be more proud" (220), Felicity Smoak saying you honor the dead by fighting and that Oliver is not done fighting (222), Tommy Merlyn saying he was wrong to call Ollie a murderer and saying that he is a hero (123), Roy Harper telling Ollie that he saved his life and gave him purpose (212) and how this time they had to save him (319), Laurel saying that she knows who Oliver is in her bones - a person who doesn't give up (221) and Robert Queen telling Oliver that "It's your responsibility now."(101)

Nate Heywood picks up Sara, Ray, Thea, Diggle and Oliver in The Waverider. He was given their coordinates by Felicity.

Ray examine the technology The Dominators were using to keep them under and determined it used a neuromorphic interface similar to what he used to control the ATOM suit. This means The Dominators may have been probing their subconscious for intel while the shared hallucination kept their minds occupied. Ray further theorizes that the five of them (Sara, Diggle, Thea, Oliver and himself) were abducted because they were ordinary humans.

Gideon translates "Klic-Clac-To Nick-Lava Shack-too" to "We are nearing completion of the weapon." Gideon further determines that the Dominator ship is moving straight for Earth.

Location

A Dominator spaceship in orbit above the Earth.

Untelevised Adventures
Cisco somehow got a piece of alien technology off of the Dominator ship that crashed in Central City. This did not happen in F308.

The Winick Factor
The subplot with Wild Dog's hatred of people with super powers comes out of nowhere, doesn't make any sense given the presence of Ragman on the same team and is far too quickly resolved.

The Bottom Line
In looking back at Arrow's past, this 100th episode reminds us of many things best forgotten. For every novel touch (i.e. the wink and nod explanation as to Tommy Merlyn's absence referencing Colin Donnell's new gigs), there are glaring absences (i.e. no Manu Bennett as Deathstroke?) and a lot of plot holes regarding how the shared dream world works. Katie Cassidy still cannot convey any emotion but annoyance convincingly and fails to emote even when offered a script that requires her to do nothing but look sexy in a towel or look sad in a wedding dress.

Despite this, the dream sequence might have worked had the whole episode been focused on it, but the cuts back to reality and the crossover only serve to distract from the drama of Sara, Oliver and Thea having to pull themselves away from their loved ones. The subplot with Wild Dog suddenly hating people with powers only to change his mind after The Flash and Supergirl save him is nearly as lame as the villain of the week. Overall, this whole episode is a bit of a mess, made tolerable only by the excellent performances of the core ensemble in the dream sequence.